Downforce is a downwards thrust created by the aerodynamic characteristics of a vehicle. The purpose of downforce is to increase the vertical force on the tires to create more road grip, thus allowing a car to travel faster through a corner. Road-going passenger cars, as well as racecars, can benefit from increased downforce. Downforce on a vehicle body is frequently achieved through use of passive devices, such as diffusers.
Generally, a diffuser is a shaped section of a vehicle underbody that is used to increase effective downforce on the vehicle. A typical diffuser improves the vehicle's aerodynamic properties by enhancing transition between high-velocity airflow underneath the car and the significantly slower free-stream airflow of the ambient atmosphere. As the vehicle moves through the air, the diffuser generally affects pressure under the vehicle body to increase effective downforce thereon.